Access to private blockchain without mining possibilities

Hello!I'm currently working on a project concerning private blockchain and I have the following:- 1 static node which is used from back-end through RPC as the Gate to blockchain (add/execute contracts)- 2 nodes for mining only

Now I would like to give access to the blockchain I'm working on to any of the users from outside. But I want to avoid any artificial intervention from them (add/execute contracts) to keep blockchain clean, basically, I would say I want to give the read-only access. So I need to prevent mining from outside and keep doing mining only through my 2 nodes and in this case users from outside don't have ethereum to add/execute contracts.

So, is there any chance to give access to the private blockchain for users from outside and keep blockchain clean and have the possibility to add/execute contracts only through my static node?